Method for forming fin field effect transistor (FINFET) device

ABSTRACT

Methods for forming a fin field effect transistor (FinFET) device structure are provided. The method includes providing a first fin structure and a second fin structure extending above a substrate and forming an isolation structure over the substrate, and the an upper portion of the first fin structure and an upper portion of the second fin structure protrudes from the isolation structure. The method also includes forming a first transistor and a second transistor on the first fin structure and the second fin structure, and the first transistor includes a first gate dielectric layer. The method further includes forming an inter-layer dielectric (ILD) structure between the first transistor and the second transistor, and a portion of the first gate dielectric layer above the isolation structure is in direct contact with a sidewall of the ILD structure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application of U.S. patent application Ser. No. 14/180,932, filed on Feb. 14, 2014, the entire of which is incorporated by reference herein.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment. Semiconductor devices are typically fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various material layers using lithography to form circuit components and elements thereon. Many integrated circuits are typically manufactured on a single semiconductor wafer, and individual dies on the wafer are singulated by sawing between the integrated circuits along a scribe line. The individual dies are typically packaged separately, in multi-chip modules, or in other types of packaging, for example.

As the semiconductor industry has progressed into nanometer technology process nodes in pursuit of higher device density, higher performance, and lower costs, challenges from both fabrication and design issues have resulted in the development of three-dimensional designs, such as the fin field effect transistor (FinFET). FinFETs are fabricated with a thin vertical “fin” (or fin structure) extending from a substrate. The channel of the FinFET is formed in this vertical fin. A gate is provided over the fin. Advantages of the FinFET may include reducing the short channel effect and higher current flow.

Although existing FinFET devices and methods of fabricating FinFET devices have been generally adequate for their intended purpose, they have not been entirely satisfactory in all aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 shows a perspective representation of a fin field effect transistor (FinFET) device structure, in accordance with some embodiments.

FIG. 2 shows a top-view of a fin field effect transistor (FinFET) device structure, in accordance with some embodiments.

FIGS. 3A-3H show cross-sectional representations of various stages of forming a fin field effect transistor (FinFET) device structure, in accordance with some embodiments.

FIGS. 4A-4F show cross-sectional representations of various stages of forming a fin field effect transistor (FinFET) device structure, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Some variations of the embodiments are described. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements. It is understood that additional operations can be provided before, during, and after the method, and some of the operations described can be replaced or eliminated for other embodiments of the method.

Embodiments for forming a fin field effect transistor (FinFET) device structure are provided. FIG. 1 shows a perspective representation of a fin field effect transistor (FinFET) device structure 100, in accordance with some embodiments of the disclosure.

FinFET device structure 100 includes a substrate 102. Substrate 102 may be made of silicon or other semiconductor materials. Alternatively or additionally, substrate 102 may include other elementary semiconductor materials such as germanium. In some embodiments, substrate 102 is made of a compound semiconductor such as silicon carbide, gallium arsenic, indium arsenide, or indium phosphide. In some embodiments, substrate 102 is made of an alloy semiconductor such as silicon germanium, silicon germanium carbide, gallium arsenic phosphide, or gallium indium phosphide. In some embodiments, substrate 102 includes an epitaxial layer. For example, substrate 102 has an epitaxial layer overlying a bulk semiconductor.

FinFET device structure 100 also includes one or more fin structures 104 (e.g., Si fins) that extend from the substrate 102. Fin structures 104 may optionally include germanium. Fin structures 104 may be formed by using suitable processes such as photolithography and etching processes. In some embodiments, fin structures 104 are etched from substrate 102 using dry etch or plasma processes.

An isolation structure 108, such as a shallow trench isolation (STI) structure, is formed to surround fin structures 104. In some embodiments, a lower portion of fin structures 104 is surrounded by isolation structure 108, and an upper portion of fin structures 104 protrudes from isolation structure 108, as shown in FIG. 1. In other words, a portion of fin structures 104 is embedded in isolation structure 108. Isolation structure 108 prevents electrical interference or crosstalk.

FinFET device structure 100 further includes a gate stack structure including a gate electrode 110 and a gate dielectric layer 106. The gate stack structure is formed over a central portion of fin structures 104. In some embodiments, multiple gate stack structures are formed over fin structures 104. Numerous other layers may also be present in the gate structures, for example, capping layers, interface layers, spacer elements, and/or other suitable features.

Gate dielectric layer 106 may include dielectric materials, such as silicon oxide, silicon nitride, silicon oxynitride, dielectric material(s) with high dielectric constant (high-k), or combinations thereof. Examples of high-k dielectric materials include hafnium oxide, zirconium oxide, aluminum oxide, hafnium dioxide-alumina alloy, hafnium silicon oxide, hafnium silicon oxynitride, hafnium tantalum oxide, hafnium titanium oxide, hafnium zirconium oxide, the like, or combinations thereof.

Gate electrode 110 may include polysilicon or metal. Metal includes tantalum nitride (TaN), nickel silicon (NiSi), cobalt silicon (CoSi), molybdenum (Mo), copper (Cu), tungsten (W), alumina (Al), cobalt (Co), zirconium (Zr), platinum (Pt), or other applicable materials. Gate electrode 110 may be formed in a gate last process (or gate replacement process). In some embodiments, the gate stack structure includes additional layers, such as interfacial layers, capping layers, diffusion/barrier layers, or other applicable layers.

Fin structures 104 includes a channel region 112 surrounded or wrapped by gate electrode 110 and gate dielectric layer 106. Fin structures 104 may be doped to provide a suitable channel for an n-type FinFET (NMOS device) or a p-type FinFET (PMOS device). Fin structures 104 may be doped using a suitable process, such as an ion implantation process, diffusion process, annealing process, other applicable processes, or combinations thereof. Fin structures 104 includes a source region 114 and a drain region 116 between the channel region 112. FinFET device 100 may be a device included in a microprocessor, memory cell (e.g., Static Random-Access Memory (SRAM)), and/or other integrated circuits.

FIG. 2 shows a top-view of a fin field effect transistor (FinFET) device structure 100, in accordance with some embodiments of the disclosure. FinFET device structure 100 includes multiple fin structures 104 and multiple gate electrodes 110. Gate electrodes 110 traverse over fin structures 104. FinFET device structure 100 is surrounded by isolation structure 108.

As shown in FIG. 2, fin structures 104 may be substantially parallel to each other. Gate electrodes 110 may also be parallel to each other and substantially perpendicular to the fin structures 104. In some embodiments, gate electrodes 110 are also called as gate electrodes lines when seen from a top-view.

A first transistor 300 a is formed on one of fin structures 104, and a second transistor 300 b is formed on another one of fin structures 104. In some embodiments, a distance (D₁) between first transistor 300 a and second transistor 300 b is in a range from about 10 nm to about 200 nm.

FIGS. 3A-3H show cross-sectional representations of various stages of forming a fin field effect transistor (FinFET) device structure, in accordance with some embodiments of the disclosure. FIGS. 3A-3H are cross-sectional representations taken along AA′ line of FIG. 2. FIGS. 3A-3H shows a gate-last process to form high-k/metal gate (HK/MG) structure.

Referring to FIG. 3A, fin structures 104 a and 104 b are formed over substrate 102. In some embodiments, the substrate 102 is etched to form fin structures 104 a and 104 b by first depositing and patterning a hard mask layer (not shown) on substrate 102. The hard mask layer forms a pattern covering a portion of substrate 102. Afterwards, substrate 102 is etched to form trenches between the regions covered by the hard mask layer. As a result, fin structures 104 a and 104 b are formed between the trenches.

Afterwards, a dielectric material (e.g., silicon oxide) is deposited into the trenches and covers fin structures 104 a and 104 b. The dielectric material is planarized down to the top surfaces of fin structures 104 a and 104 b or the hard mask layer, and then the dielectric material is etched to a level below the top surfaces of fin structures 104 a and 104 b. As a result, an upper portion of fin structures 104 a and 104 b protrudes above isolation structure 108, and a lower portion of fin structures 104 a and 104 b is surrounded and covered by isolation structure 108.

Alternatively, in some other embodiments, isolation structure 108 is firstly formed over substrate 102. Trenches between isolation structure 108 are formed to expose substrate 102. A semiconductor material, such as silicon, silicon germanium, or other applicable materials, is then grown in the trenches to form fin structures 104 a and 104 b by using, for example, an epitaxial process. After fin structures 104 a and 104 b are grown to the desired height, isolation structure 108 is etched down to a level below the top surface of fin structures 104. As a result, a portion of fin structures 104 a and 104 b protrudes above isolation structure 108.

As shown in FIG. 3A, a polysilicon layer 302 is formed on fin structures 104 a and 104 b and isolation structure 108. Afterwards, one or more hard masks 304 a, 304 b are formed over polysilicon layer 302. Hard mask 304 a may be made of silicon oxide, silicon nitride, silicon oxynitride, or other applicable materials. Hard mask 304 b may be made of silicon oxide, silicon nitride, silicon oxynitride, or other applicable materials. Hard masks 304 a, 304 b are formed by a patterning process. The patterning process includes a photolithography process and an etching process. The photolithography processes include photoresist coating (e.g., spin-on coating), soft baking, mask aligning, exposure, post-exposure baking, developing the photoresist, rinsing and drying (e.g., hard baking). The etching process includes a dry etching process or a wet etching process.

After forming hard masks 304 a and 304 b, a portion of polysilicon layer 302 are removed by using hard masks 304 a and 304 b as a mask as shown in FIG. 3B in accordance with some embodiments of the disclosure. In some embodiments, polysilicon layer 302 is removed by an etching process, such as a wet etching process or a dry etching process. It should be noted that although in FIG. 3B, polysilicon layer 302 is remaining when seen from other cross-sectional views, a portion of polysilicon layer 302 is removed.

Afterwards, polysilicon layer 302 is removed to form a trench 303 as shown in FIG. 3C in accordance with some embodiments of the disclosure. In some embodiments, polysilicon layer 302 is removed by an etching process, such as a wet etching process or a dry etching process.

After polysilicon layer 302 is removed, a gate dielectric layer 306 is conformally formed on fin structures 104 a and 104 b as shown in FIG. 3D in accordance with some embodiments of the disclosure.

Gate dielectric layer 306 includes high dielectric constant (high-k) dielectric materials. Examples of high-k dielectric materials include hafnium oxide, zirconium oxide, aluminum oxide, hafnium dioxide-alumina alloy, hafnium silicon oxide, hafnium silicon oxynitride, hafnium tantalum oxide, hafnium titanium oxide, hafnium zirconium oxide, or the like. In some embodiments, gate dielectric layer 306 is formed by deposition processes, such as a CVD process, HDPCVD process, spin-on process, sputtering process, and/or combinations thereof.

Gate electrode 308 includes n-type work function metal or p-type work function metal. The n-type work function metal includes tungsten (W), copper (Cu), titanium (Ti), silver (Ag), aluminum (Al), titanium aluminum alloy (TiAl), titanium alumina nitride (TiAlN), tantalum carbide (TaC), tantalum carbon nitride (TaCN), tantalum silicon nitride (TaSiN), manganese (Mn), or zirconium (Zr). The p-type work function metal includes titanium nitride (TiN), tungsten nitride (WN), tantalum nitride (TaN), or ruthenium (Ru). Gate electrode 308 is formed by a physical vapor deposition (PVD) process, chemical vapor deposition (CVD) process, plating process, electroless plating process or another applicable process.

After gate electrode 308 is formed, a photoresist (PR) layer 310 is formed on gate electrode 308 as shown in FIG. 3E in accordance with some embodiments of the disclosure. In some embodiments, first PR layer 310 is a positive resist (positive tone resist). The positive resist is characterized by the exposed regions becoming more soluble in a developer solution.

As shown in FIG. 3E, after photoresist layer 310 is formed, photoresist layer 310 is patterned by a patterning process to form an opening 311 in patterned photoresist layer 310. The patterning process includes a photolithography process and an etching process. The photolithography processes include photoresist coating (e.g., spin-on coating), soft baking, mask aligning, exposure, post-exposure baking, developing the photoresist, rinsing and drying (e.g., hard baking). The etching process includes a dry etching process or a wet etching process.

After forming opening 311, gate electrode 308 is etched by an etching process to form a trench 312 in gate electrode 308 as shown in FIG. 3F in accordance with some embodiments of the disclosure. In some embodiments, the etching process includes a dry etching process or wet etching process.

On the left side of trench 312, a first transistor 300 a is constructed by gate dielectric layer 306, gate electrode 308, and a source/drain (not shown). On the right side of trench 312, a second transistor 300 b is constructed by gate dielectric layer 306, gate electrode 308, and another source/drain (not shown).

After trench 312 is formed, a dielectric material 314 is filled into trench 312 and on gate electrode 308 as shown in FIG. 3G in accordance with some embodiments of the disclosure.

After dielectric material 314 is filled, a portion of dielectric material 314 out of trench 312 is removed by a planarizing process as shown in FIG. 3H in accordance with some embodiments of the disclosure. As a result, an inter-layer dielectric (ILD) structure 316 is formed. First transistor 300 a and second transistor 300 b are on opposite sidewalls of ILD structure 316. When seen from other cross-sectional views, gate electrode 308 is surrounded by the ILD structure 316.

In some embodiments, a top surface of gate electrode 308 is substantially level with a top surface of first transistor 300 a and second transistor 300 b. In some embodiments, the planarizing process includes a chemical mechanical polishing (CMP) process or another applicable process.

In some embodiments, ILD structure 316 has a width W₁ in a range from about 10 nm to about 200 nm. In some embodiments, a distance (D₁) between the sidewall of ILD structure 316 and a sidewall of first fin structure 104 b is in a range from about 5 nm to about 50 nm.

If an ILD structure is formed next to a fin structure before a gate dielectric layer is formed on the fin structure, a trench is formed between two the protrusions (the ILD structure and the fin structure). When the distance between the ILD structure and the fin structure is reduced, a high aspect ratio of the trench is formed. Therefore, when the gate dielectric layer and a gate electrode are formed on the fin structure, some voids tend to be formed in the trench due to its high aspect ratio. In addition, the voids problems become more serious as the dimensions of a semiconductor device structure are gradually decreased. Furthermore, when multiple dielectric layers are sequentially and conformally formed on fin structures and on the sidewalls of the ILD structure, voids are easily formed in the trench. The voids may increase a resistance (e.g. Rs) of the semiconductor device structure. As a result, the performance of the semiconductor device structure may be degraded.

In order to resolve the void problem, ILD structure 316 is formed after gate dielectric layer 306 and gate electrode 308 are formed. In other words, ILD structure 316 is formed after first transistor 300 a and second transistor 300 b are formed.

It should be noted that, as shown in FIG. 3H, gate dielectric layer 306 and gate electrode 308 are in direct contact with the sidewalls of ILD structure 316. More specifically, gate dielectric layer 306 covers a bottom portion of the sidewalls of ILD structure 316, and gate electrode 308 covers a top portion of the sidewalls of ILD structure 316. ILD structure 316 is directly sandwiched between two adjacent gate electrodes 306 (or first transistor 300 a or second transistor 300 b). Gate dielectric layer 306 does not cover the overall sidewalls of ILD structure 316.

Because ILD structure 316 is formed after first transistor 300 a and second transistor 300 b are formed, an etching process window for forming trench 312 is enlarged. In addition, the filling windows for forming gate dielectric layer 306 and gate electrode 308 are therefore enlarged.

FIGS. 4A-4F show cross-sectional representations of various stages of forming a fin field effect transistor (FinFET) device structure, in accordance with some embodiments of the disclosure.

Referring to FIG. 4A, polysilicon layer 302 is removed to form trench 303. FIG. 4A is similar to FIG. 3C, and so detailed descriptions are omitted for brevity.

After trench 303 is formed, a high-k gate dielectric layer 412 is conformally formed on fin structures 104 a and 104 b as shown in FIG. 4B in accordance with some embodiments of the disclosure. High-k gate dielectric layer 412 includes hafnium oxide, zirconium oxide, aluminum oxide, hafnium dioxide-alumina alloy, hafnium silicon oxide, hafnium silicon oxynitride, hafnium tantalum oxide, hafnium titanium oxide, hafnium zirconium oxide, or the like. In some embodiments, high-k gate dielectric layer 412 is formed by deposition processes, such as a CVD process, HDPCVD process, spin-on process, sputtering process, or other applicable processes.

After forming high-k gate dielectric layer 412, diffusion barrier layer 414 is conformally formed on high-k gate dielectric layer 412. Diffusion barrier layer 414 inhibits diffusion of the metal that will be formed later.

Afterwards, a work function layer 416 is formed on diffusion barrier layer 414 and fin structure 104 a. Work function layer 416 helps tune a work function for a PMOS transistor. Therefore, a desired threshold voltage is achieved for the PMOS transistor. In some embodiments, work function layer 416 is a p-type work function metal including titanium nitride (TiN), tungsten nitride (WN), tantalum nitride (TaN), or ruthenium (Ru).

Afterwards, on fin structure 104 a, a block layer 418 is formed on work function layer 416. On fin structure 104 b, block layer 418 is formed on diffusion barrier layer 414. Block layer 418 is configured to block or reduce diffusion between the layer below (e.g. work function layer 416) and the layer above (e.g. a metal fill layer).

Metal fill layer 420 is formed on block layer 418. Therefore, on fin structure 104 a, a first gate electrode is constructed by work function layer 416, block layer 418 and metal fill layer 420. On fin structure 104 b, a second gate electrode is constructed by block layer 418 and metal fill layer 420. Metal fill layer 420 is configured to serve as the main conductive portion of gate electrode. In some embodiments, metal fill layer 420 includes conductive materials, such as aluminum (Al) or titanium (Ti), tungsten (W), copper (Cu), or combinations thereof.

After metal fill layer 420 is formed, photoresist (PR) layer 310 is formed on metal fill layer 420 shown in FIG. 4C in accordance with some embodiments of the disclosure. Afterwards, PR layer 310 is patterned to form opening 311 in patterned photoresist layer 310.

After PR layer 310 is patterned, gate dielectric layer 412, diffusion barrier layer 414, work function layer 416, block layer 418 and metal fill layer 420 are etched by an etching process to form a trench 312 in gate electrode 308 as shown in FIG. 4D in accordance with some embodiments of the disclosure. In some embodiments, the etching process includes a dry etching process or wet etching process.

On the left side of trench 312, a first transistor 400 a is constructed by high-k gate dielectric layer 412, diffusion barrier layer 414, work function layer 416, block layer 418 and metal fill layer 420 and a source/drain (not shown). On the right side of trench 312, a second transistor 400 b is constructed by high-k gate dielectric layer 412, diffusion barrier layer 414, block layer 418 and metal fill layer 420, and another source/drain (not shown). In some embodiments, first transistor 400 a is a PMOS device, and second transistor 400 b is a NMOS device.

After trench 312 is formed, a dielectric material 314 is filled into trench 312 and on metal fill layer 420 as shown in FIG. 4E in accordance with some embodiments of the disclosure.

After dielectric material 314 is filled, a portion of dielectric material 314 out of trench 312 is removed by a planarizing process as shown in FIG. 4F in accordance with some embodiments of the disclosure. As a result, an inter-layer dielectric (ILD) structure 316 is formed. First transistor 400 a and second transistor 400 b are on opposite sidewalls of ILD structure 316.

Embodiments for forming fin field effect transistor (FinFET) device structure are provided. A fin structure is formed on a substrate. A gate dielectric layer and a gate electrode are sequentially formed on the fin structure to form a transistor on the fin structure. An inter-layer dielectric (ILD) structure is formed after the transistor is formed. Problems with forming the gate dielectric layer and gate electrode in a limited distance between the fin structure and the ILD structure are reduced by changing the fabricating operation of the ILD structure. Therefore, the etching process window for forming a trench for filling the ILD structure is enlarged. In addition, the filling windows for forming the gate dielectric layer and the gate electrode are therefore enlarged.

In some embodiments, a fin field effect transistor (FinFET) device structure is provided. The method includes providing a first fin structure and a second fin structure extending above a substrate and forming an isolation structure over the substrate, and the an upper portion of the first fin structure and an upper portion of the second fin structure protrudes from the isolation structure. The method also includes forming a first transistor and a second transistor on the first fin structure and the second fin structure, and the first transistor includes a first gate dielectric layer. The method further includes forming an inter-layer dielectric (ILD) structure between the first transistor and the second transistor, and a portion of the first gate dielectric layer above the isolation structure is in direct contact with a sidewall of the ILD structure.

In some embodiments, a fin field effect transistor (FinFET) device structure is provided. The method includes providing a first fin structure and a second fin structure extending above a substrate, and conformally forming a high-k gate dielectric layer on the first fin structure and the second fin structure. The method further includes forming a gate electrode on the high-k gate dielectric layer, and a first transistor is constructed by the high-k gate dielectric layer and the gate electrode above the first fin structure, and a second transistor is constructed by the high-k gate dielectric layer and the gate electrode above the second fin structure. The method further includes forming an inter-layer dielectric (ILD) structure between the first transistor and the second transistor, and the ILD structure is formed after the high-k gate dielectric layer is formed.

In some embodiments, a method for forming a fin field effect transistor (FinFET) device structure is provided. The method includes providing a first fin structure and a second fin structure extending above a substrate, and forming a gate dielectric layer on the first fin structure and the second fin structure. The method further includes forming a metal fill layer on the first fin structure and the second fin structure and removing a portion of the gate dielectric layer and a portion of the metal fill layer to form a trench between the first fin structure and the second fin structure. The method also includes forming an inter-layer dielectric (ILD) structure in the trench, and a portion of the metal fill layer is in direct contact with a sidewall of the ILD structure.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method for forming a fin field effect transistor (FinFET) device structure, comprising: providing a first fin structure and a second fin structure extending above a substrate; forming an isolation structure over the substrate, wherein an upper portion of the first fin structure and an upper portion of the second fin structure protrudes from the isolation structure; forming a first transistor and a second transistor on the first fin structure and the second fin structure, wherein the first transistor comprises a first gate dielectric layer; and forming an inter-layer dielectric (ILD) structure between the first transistor and the second transistor, wherein a portion of the first gate dielectric layer above the isolation structure is in direct contact with a sidewall of the ILD structure.
 2. The method for forming the FinFET device structure as claimed in claim 1, further comprising: forming a polysilicon layer on the first fin structure and the second fin structure before forming the first transistor and the second transistor on the first fin structure and the second fin structure.
 3. The method for forming the FinFET device structure as claimed in claim 2, further comprising: removing the polysilicon layer to form a recess; and filling the first gate dielectric layer in the recess and on the first fin structure and the second fin structure.
 4. The method for forming the FinFET device structure as claimed in claim 3, further comprising: forming a first gate electrode on the first gate dielectric layer and in the recess, wherein a portion of the first gate electrode is in direct contact with a top portion of the ILD structure.
 5. The method for forming the FinFET device structure as claimed in claim 1, wherein forming the ILD structure between the first transistor and the second transistor comprises: forming a trench between the first transistor and the second transistor; filling a dielectric material into the trench and on the first transistor and the second transistor; and removing a portion of the dielectric material to expose the first transistor and the second transistor, wherein the ILD structure is formed between the first transistor and the second transistor.
 6. The method for forming the FinFET device structure as claimed in claim 5, wherein a portion of the first transistor and a portion of second transistor are exposed by the trench.
 7. A method for forming a fin field effect transistor (FinFET) device structure, comprising: providing a first fin structure and a second fin structure extending above a substrate; conformally forming a high-k gate dielectric layer on the first fin structure and the second fin structure; forming a gate electrode on the high-k gate dielectric layer, wherein a first transistor is comprises the high-k gate dielectric layer and the gate electrode above the first fin structure, and a second transistor comprises the high-k gate dielectric layer and the gate electrode above the second fin structure; and forming a dielectric structure between the first transistor and the second transistor, wherein the dielectric structure is formed after the high-k gate dielectric layer is formed, and the first transistor and the second transistor are separated by the dielectric structure.
 8. The method for forming the FinFET device structure as claimed in claim 7, further comprising: forming a dummy gate electrode on the first fin structure and the second fin structure before conformally forming the high-k gate dielectric layer on the first fin structure and the second fin structure.
 9. The method for forming the FinFET device structure as claimed in claim 8, further comprising: removing the dummy gate electrode to form a recess; and forming the high-k gate dielectric layer in the recess.
 10. The method for forming the FinFET device structure as claimed in claim 7, wherein forming the dielectric structure between the first transistor and the second transistor comprises: forming a photoresist layer on the gate electrode; patterning the photoresist layer to form a patterned photoresist layer; etching a portion of the gate electrode and a portion of the high-k gate dielectric layer by using the patterned photoresist layer as a mask to form a trench in the gate electrode and the high-k gate dielectric layer.
 11. The method for forming the FinFET device structure as claimed in claim 10, further comprising: filling a dielectric material into the trench and on the gate electrode.
 12. The method for forming the FinFET device structure as claimed in claim 11, further comprising: performing a planarizing process on the dielectric material to expose a top surface of the gate electrode.
 13. The method for forming the FinFET device structure as claimed in claim 7, further comprising: forming an isolation structure on the substrate, wherein an upper portion of the first fin structure and an upper portion of the second fin structure protrudes from the isolation structure; and forming the dielectric structure on the isolation structure, wherein a portion of the high-k dielectric layer is in direct contact with a bottom portion of the dielectric structure.
 14. The method for forming the FinFET device structure as claimed in claim 7, wherein forming the gate electrode on the high-k gate dielectric layer comprises: forming a diffusion barrier layer on the high-k gate dielectric layer; forming a block layer on the diffusion barrier layer; and forming a metal fill layer on the block layer.
 15. The method for forming the FinFET device structure as claimed in claim 14, further comprising: forming a work function layer between the diffusion barrier layer and the block layer on the first fin structure.
 16. A method for forming a fin field effect transistor (FinFET) device structure, comprising: providing a first fin structure and a second fin structure extending above a substrate; forming a gate dielectric layer on the first fin structure and the second fin structure; forming a metal fill layer on the first fin structure and the second fin structure, wherein a first transistor comprises the gate dielectric layer and the metal fill layer above the first fin structure, and a second transistor comprises the gate dielectric layer and the metal fill layer above the second fin structure; removing a portion of the gate dielectric layer and a portion of the metal fill layer to form a trench separating the first transistor and the second transistor; and forming a dielectric structure in the trench, wherein a portion of the metal fill layer is in direct contact with a sidewall of the dielectric structure.
 17. The method for forming the FinFET device structure as claimed in claim 16, further comprising: forming an isolation structure over the substrate, wherein the a bottom portion of the first fin structure and a bottom portion of the second fin structure are embedded in the isolation structure; and forming the dielectric structure on the isolation structure.
 18. The method for forming the FinFET device structure as claimed in claim 16, further comprising: forming a work function layer between the gate dielectric layer and the metal fill layer on the first fin structure, wherein a portion of the work function layer is in direct contact with the dielectric structure.
 19. The method for forming the FinFET device structure as claimed in claim 16, wherein forming the dielectric structure in the trench comprises: forming a dielectric material in the trench and on the metal fill layer; and removing a portion of the dielectric material to expose a top surface of the metal fill layer.
 20. The method for forming the FinFET device structure as claimed in claim 16, further comprising: forming a photoresist layer on the metal fill layer before removing the portion of the gate dielectric layer and the portion of the metal fill layer; patterning the photoresist layer to form a patterned photoresist layer; and removing the portion of the metal fill layer and the portion of the metal fill layer by using the patterned photoresist layer as a mask. 